The invention relates generally to gas lasers, and more particularly to a fine-adjust mechanism or micropositioner for the mirrors of such a laser, enabling extremely fine adjustments with little backlash.
An essential component of a laser is an optical cavity consisting of two opposing mirrors on either end of the laser. These mirrors cause light emitted from an excited gas to resonate between them. To establish maximum power output, the mirrors must be in precise angular alignment, on the order of ten microradians. Unfortunately, the tolerances associated with the manufacture of the optical cavity do not permit such a precise assembly to be set during manufacture. As a result, it is necessary to provide the user with a fine-tuning device which positions one of the mirrors to the designed alignment. This invention is directed to an improved fine-tuning device.
A typical micropositioner which has been in current use had the mirror to be aligned mounted on a plate at the end of the optical cavity. The plate was spring loaded, bearing against three thermally stable quartz rods which minimized changes in alignment due to variations in ambient temperature.
The necessary angular alignment of the mirror was obtained by turning a fine-adjustment knob, the rotation of which was geared down by a factor of sixty. The geared-down output acted as an input to an extra-fine screw that converted the rotary motion of the reduction gears to a linear motion which in turn tilted the mirror plate relative to the quartz rods. This resulted in an angular displacement of the mirror about a pivot point, causing a change in laser power output.
There have been two primary problems with this type fine-adjustment systems:
(a) Gear backlash. Backlash in the rotary gear reduction system described has resulted in mirror alignment which is neither resetable nor repeatable.
(b) Screw imperfections. Laser power output was directly coupled to the linear motion of the extra-fine screw used in the above-described design. As a result, any manufacturing imperfections in the screw such as shaft eccentricities or poor surface finish would result in undesirable changes in the output.